1. Field of the Invention
The present invention relates to a spontaneous light-emissive flat panel-type image display device and, more particularly, to a panel structure suitable for an image display device having a rear panel which comprises a substrate having a main surface and thin film type-electron sources disposed in the form of a matrix on the main surface of the substrate.
2. Description of the Related Art
As one example of spontaneous light-emissive flat panel-type display devices having electron sources two-dimensionally arranged in the form of a matrix, there is known a display device which employs an electron-emissive flat panel utilizing a cold cathode which is micro and can be integrated. As the cold cathode which is one of elements constituting the electron-emissive flat panel, there is known a thin film electron source such as a spint-type electron source, a surface conductive-type electron source, a carbon nano tube type electron source, an MIM (Metal Insulator Metal) type electron source in which a layer of metal, a layer of an insulator and a layer of metal are stacked, an MIS (Metal-Insulator-Semiconductor)-type electron source in which a layer of metal, a layer of an insulator and a layer of a semiconductor are stacked, and a metal-insulator-semiconductor-metal type electron source.
A driver circuit and the like are combined with the panel provided with such electron sources, to thereby form an image display device.
FIG. 1 is a schematic view which is of assistance in explaining a display principal for one pixel in a display panel which is one of elements constituting an image display device which employs MIM-type electron sources. This display panel includes a rear panel PNL1 and a front panel PNL2. The rear panel PNL1 and the front panel PNL2 are hermetically combined with each other by a closure frame not shown, whereby an internal space of the display panel is kept in an evacuated condition. The rear panel PNL1 includes a rear substrate SUB1 having a main surface and formed from, for example, a glass substrate or the like, an image signal wire d (a so-called data wire) provided on the main surface of the rear substrate SUB1 and constituting a lower electrode for an electron source, the image signal wire d being suitably formed of an aluminum (Al) film, a first insulating film INS1 formed of an anode oxidation film formed by causing the aluminum of the lower electrode to be anode-oxidized, a second insulating film INS2 suitably formed of a silicon nitride (SiN) film, an electric supply electrode (connection electrode) ELC, a scan signal wire s suitably formed of aluminum (Al), and an upper electrode AED connected to the scan signal wire s and being one of elements constituting the electron source for the pixel.
The electron source ELS utilizes the image signal wire d as the lower electrode and includes a thin film portion INS3 constituting a part of the first insulating film INS1 disposed on the lower electrode and a portion constituting a part of the upper electrode AED disposed on the thin film portion INS3. The upper electrode AED is formed so as to cover the scan signal wire s and a part of the electric supply electrode ELC. The thin film portion INS3 is a so-called tunnel film. By this structure, a so-called diode electron source is formed.
On the other hand, the front panel PNL2 includes a front substrate SUB2 having a main surface and suitably formed from a transparent glass substrate, a shading film (hereinafter referred to as “black matrix”) BM disposed on the main surface of the front substrate SUB2, a phosphor PH separated from adjacent pixels by the shading film BM, and an anode AD suitably formed of an aluminum deposition film.
A spacing between the rear panel PNL1 and the front panel PNL2 is approximately 3-5 mm and is kept constant by a spacer SPC called a bulkhead. The thicknesses of the rear substrate SUB1 and the front substrate SUB2 are about 2.8 mm, for example. The height of the spacer is about 3 mm, for example. Spacer SPC are provided for every scan signal wires s so as to continuously or discontinuously stand up from the scan signal wires s. While the thicknesses of the respective layers are shown in FIG. 1 so as to be emphasized for clarity, the thickness of the film constituting the scan signal wire s is about 3 μm, for example.
In the image display panel constructed as discussed above, when accelerating voltage V (about 2 kV to 10 kV, and about 5 kV in the illustrated example) is applied between the upper electrode AED of the rear panel PNL1 and the anode AD of the front panel PNL2, a bundle EB of electrons e− (electron bundle or electron beam) corresponding to the magnitude of display data supplied to the image signal wire d which is the lower electrode is emitted. The electron bundle EB is bombarded against the phosphor PH by the accelerating voltage V and excites the phosphor PH, whereby the phosphor PH emits light L of a predetermined frequency out of the front panel PNL2. Incidentally, when full-color display is to be performed, this unit pixel is a sub-pixel for color and one color pixel is typically comprised of three sub-pixels, i.e., a red (R) sub-pixel, a green (G) sub-pixel and a blue sub-pixel.
The spacer SPC is formed from a thin plate of glass or ceramics. Therefore, the spacer which is arranged in the vicinity of the electron source ELS is charged by parts of the electrons emitted from the electron source and emits secondary electrons, whereby the electron bundle EB is deflected as indicated in FIG. 1 by arrows D. The magnitude of this deflection becomes larger the more the electron source is close to the spacer. Moreover, electron bundles emitted from electron sources which are arranged in the vicinity of an end portion SEG of the spacer (see FIG. 2) are deflected in such directions as to take the shortest distance with respect to the end portion SEG.
FIG. 2 is a schematic layout of phosphors on the main surface of the front substrate, which is of assistance in explaining variations in landing of electron bundles from electron sources on the phosphors which occur due to the deflection of the electron bundles which is brought about by the spacer. FIG. 3 is a schematic sectional view of the display panel including the rear substrate, taken along the line B-B′ in FIG. 2. The front substrate SUB2 has the black matrix BM disposed on the main surface thereof and the phosphors PH (red, green and blue phosphors R, G, B) applied into openings of the black matrix BM. Incidentally, the anode AD shown in FIG. 1 has been left out of the illustration. The spacer SPC is arranged along the unshown scan signal wire. The openings of the black matrix into which the phosphors PH are applied (the openings are filled with the phosphors, so that a relationship between the openings and the phosphors is represented as the openings=phosphors PH) are disposed at equal pitches in a longitudinal direction X of the spacer and in a direction Y perpendicular to the longitudinal direction X. FIG. 3 also illustrates that electron sources ELS provided on the rear substrate SUB1 are arranged at equal pitches PV in the direction Y.
Of the electron bundles EB which are emitted from the electron sources ELS provided on the rear substrate SUB1 and indicated in FIGS. 2 and 3 by broken lines, electron bundles emitted from electron sources which are arranged adjacent the spacer SPC are particularly greatly affected by the electrification of the spacer SPC. In FIG. 2, deflection directions of the electron bundles EB and the magnitude of the deflection are illustrated by thick arrows. Incidentally, as shown in FIGS. 2 and 3, the spacer SPC is arranged so as to extend in the longitudinal direction X at a center portion between two lines of electron sources ELS which are arranged on the left hand side of the sheets of these Figures, and a spacer is not arranged in the right direction or in the direction Y in which two or more lines of electron sources ELS shall be arranged.
Of the electron bundles EB which are emitted from the electron sources ELS and shown in the shape of a rectangle in FIG. 2 by broken lines, the more electron bundles are close to the spacer, the deflection amounts of the electron bundles become large. Such electron bundles are shifted relative to corresponding openings of the black matrix, namely, corresponding phosphors PH. As a result, regions which are not excited by the electron bundles (do not emit light) are produced in the corresponding phosphors, thus presenting on a screen black stripes extending the longitudinal direction X of the spacer. This results in considerable deterioration of a display quality and leads to an irregularity in the brightness of the screen.